The invention refers to a clamping device for a tool at a machine tool, particularly a die sinking electric discharge machine. Such machine is equipped with a chuck having two pairs of rails projecting from the underside of the chuck and arranged in a rectangular cross. The rails are provided with reference surfaces for adjusting the tool with respect to an x-direction and a y-direction relative to the machine tool, said directions extending transversely to a center line of the chuck.
A coupling device is known from No. 4,615,688 which may also be utilized at a die sinking electric discharge machine for working a workpiece by spark erosion by means of an electrode. In the known coupling device the electrode has to be coupled to the chuck of a quill of the die sinking electric discharge machine. In a die sinking electric discharge machine a fixed system of coordinates is defined, the x-y-plane of which extends transversely to the movement of the quill which may be moved up and down in z-direction. For positioning the electrode in the system of coordinates by the known coupling device posts having reference surfaces are set upon the tool which abut against a surface of the chuck for adjustment in z-direction when clamping the tool. Moreover, the underside of the chuck is provided with prismatic bars engaging in slots of a center plate for positioning the electrode within the x-y-plane. The center plate is arranged between the electrode and the chuck. A central pin of the chuck penetrates into a center hole and an eccentric pin into a slot of the center plate for centering and axially aligning said plate.
While the known coupling device shows means for aligning and centering a tool within the system of machine coordinates, it does not provide for means which allow clamping and unclamping of the tool to the chuck. Such clamping means, however, represent an important portion of the over-all coupling device because it has to support a great tool weight and to urge the tool into engagement with the aligning means. Otherwise, the desired repeatability of exact alignment is not maintained. On the other hand, the clamping means should allow for rapid and easy locking and unlocking to facilitate an exchange of electrodes.